# I have a rather large matrix. The data was sampled at 100 Hz. I want to the data to look like it was sampled at 5 Hz

4 views (last 30 days)
Todd on 17 Aug 2012
Right now the left column is time and it counts .01, .02, .03 etc.
I want to pull out all of the data at 5 hz intervals such as 0, .2, .4 and delete the rest of the rows.
I will answer any question for clarification too
Jürgen on 18 Aug 2012
yeah all right all depends on what you are measuring and the first thing to do is to analyse your data in a smart way of course, but let us say that you are doing e.g. loadcell measurements over time to see how a the force changes, you will have noise on the measurement and the average will gie you an idea how the signal moves in time , that is what I meant

Jürgen on 17 Aug 2012
well If I understand it well you have a vector Sample100 with 100 Hz Samples and you want only the sample @ 5 hz Sample5=Sample100(1:20:end) should do the trick then hope this helps regards,J

Azzi Abdelmalek on 17 Aug 2012
Edited: Azzi Abdelmalek on 17 Aug 2012
fe=100 %sample frequency
te=1/fe %sample time
t=0:te:1;y=rand(length(t),1)%
fd=5 %desired frequency
td=1/fd %desired sample time
nt=floor(td/te)
ind=1:nt:length(t);
new_t=t(ind);
new_y=y(ind);
plot(t,y);hold on;plot(new_t,new_y,'xr','linewidth',14);

Matt Fig on 17 Aug 2012
Here is another example. You say the first column is time, so it is here.
% Original data with columns: [time,signal]
S = [(0:.01:2*pi).' sin(0:.01:2*pi).'];
Sd = S(1:20:end,:); % Downsampled signal.
plot(S(:,1),S(:,2),'b.',Sd(:,1),Sd(:,2),'sr')
legend('Original','Downsampled')

Dr. Seis on 17 Aug 2012
Edited: Dr. Seis on 17 Aug 2012
Use resample - This is an example of why you may not want to take every Nth amplitude:
Example where a is your input dataset and b is your output dataset:
Fs_in = 100; % samples per second
Fs_out = 5; % samples per second
b = resample(a,Fs_out,Fs_in);

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